The proposed study involves the establishment of a large cohort of fertile adult twins ascertained through their offspring by a survey of collaborating school systems. The 300 twin pairs - 100 monozygotic (MZ) females, 50 MZ males, 100 dizygotic (DZ) females and 50 DZ males - their spouses and offspring will be included in studies of blood pressure and pulmonary function. Specifically, the study is designed to assess some of the environmental and genetic components of variance of these physiological measures, both of which are importantly related to chronic diseases in aging populations. Families of adult twins contain all of the necessary genetic and environmental relationships to accomplish this goal. An iterative weighted least squares analysis is used to identify relevant sources of genetic (additive, dominance, etc.), environmental (within-sibships, among sibships, etc.), and maternal effects, if they exist. Further intensive study and manipulation of these identifiable sources of environmental variation may lead to the eventual anticipation or prevention of the disease state.